On three-layer coextrusion blown-film lines configured with a 65 mm grooved-feed extruder and a 350 mm spiral mandrel die, CHN Energy Ningxia Coal LLDPE 7042 is processed in the inner and core layers for industrial liners and heavy-duty sacks at layer distributions of 20/60/20 or 30/40/30, depending on seal-integrity requirements. The resin, with a nominal melt index of 1.8–2.2 g/10 min per ASTM D1238 and density of 0.918–0.922 g/cm³ per ASTM D1505, is dry-blended with 15–30 wt% high-pressure LDPE having a 0.25–0.35 g/10 min melt index to increase bubble stability and reduce neck-in. Barrel temperatures from feed zone to metering zone follow a rising profile of 170 °C, 185 °C, 195 °C, and 200 °C; melt pressure at the adapter is held between 30 MPa and 38 MPa at 80–100 rpm screw speed. Pressure oscillation exceeding ±1.0 MPa generally indicates feed bridging in the grooved intake zone when ambient dew point rises above 18 °C and resin is conveyed directly from outdoor silos. Die gap is set at 1.4–2.0 mm, blow-up ratio is maintained within 2.8:1–3.5:1, and frost line height is positioned 5–8 die diameters above the lips. Film produced at 120–200 µm exhibits machine-direction tensile strength at break per ASTM D882 of 25–35 MPa and transverse-direction tensile strength of 20–28 MPa, with elongation at break of 500–750% at a crosshead speed of 500 mm/min. Dart drop impact per ASTM D1709 Method A for a 150 µm three-layer structure is typically not less than 150 g at 23 °C. Seal strength on side-gusset sacks is evaluated per ASTM F88 at 80–110 N/25 mm when the inner layer is formulated from 100% 7042 and jaw temperature is held at 135–150 °C. Surface condensation from resin stored in unheated warehouses with relative humidity above 80% should be removed with a desiccant hopper at 65 °C for 2 h before extrusion; otherwise gel speck formation increases in the outer film surfaces. Non-food industrial liners are normally assessed against REACH and the RoHS Recast 2011/65/EU; food-contact sack liners fall under FDA 21 CFR 177.1520 and EU 10/2011 when the final migration test per EN 1186 yields an overall migration value below 10 mg/dm². The continuous service temperature should not exceed 65 °C, and the material is not suitable for hot-fill packaging above 85 °C.

Why Does 7042 Function as the Core Layer in Cast Stretch Film Without Reducing Machine-Direction Elongation?

Cast stretch film operations select 7042 for the core layer in A/B/A coextrusion at 70–85 wt% of the structure, with cling skins containing metallocene LLDPE, EVA, or polyisobutylene-modified compounds. The cast process uses a 100–150 mm barrier screw extruder, a flat die gap of 0.5–1.0 mm, and chill rollers maintained at 15–30 °C. Line speeds of 300–600 m/min are achievable because the 2.0 g/10 min melt index of 7042 reduces head pressure and extruder motor load relative to fractional-melt LLDPE. Drawdown to 10–20 µm thickness requires controlled neck-in; neck-in is reduced by blending 10–20 wt% high-pressure LDPE or by positioning the air-knife assembly to create an air gap of 5–15 mm. Puncture resistance is determined per ASTM D5748; a 20 µm film containing 80 wt% 7042 and 20 wt% metallocene LLDPE typically shows puncture energy values of 0.8–1.2 J depending on additive loading and cooling-roll temperature. Cling performance is measured per ASTM D5458, with a peel force on the cling skin of 0.5–0.9 N/cm; the cling layer is not produced from 7042 alone but requires 0.5–1.5 wt% polyisobutylene masterbatch or an EVA skin layer. Pre-stretch on pallet-wrapping equipment is limited to 200–300%; above this range, or at ambient temperatures below 10 °C, the butene comonomer architecture of 7042 increases elastic recovery and reduces holding-force retention when assessed by ISO 527-3 hysteresis cycling. Processing conflicts arise when the corona treater is run above 42 mN/m, because excessive surface oxidation increases blocking after roll storage at 35 °C for 48 h. Published data for the specific CHN Energy Ningxia Coal 7042 formulation in high-cling multilayer cast films is limited; incoming lot verification by ASTM D1238, ASTM D1505, and film tear testing per ASTM D1922 is required when the resin source or additive package is changed.

Where photooxidative service life beyond 24 months is required, 7042 is used in three-layer greenhouse film with a layer ratio of 25/50/25 and a total thickness of 150–200 µm. The outer layer is compounded with 0.3–0.6 wt% hindered amine light stabilizer masterbatch, 0.1–0.3 wt% benzotriazole UV absorber, and 2–3 wt% titanium dioxide white or carbon black masterbatch for light diffusion. The middle layer contains 10–15 wt% EVA with 14–18% vinyl acetate to improve infrared retention and night-time heat conservation. Processing on a 50 mm three-layer blown-film line with a 200 mm die uses a blow-up ratio of 2.0:1–3.0:1 and a melt temperature of 180–200 °C, the lower range being selected to limit EVA degradation and acid formation in the middle layer. Light transmission and haze are assessed per ASTM D1003; total visible light transmission in unpigmented UV-stabilized film at 160 µm is normally above 88%. Anti-fog performance is assessed by the condensation test method in EN 13206, with glycerol ester anti-drip masterbatch let-down of 0.5–1.0 wt%. Pesticide compatibility is a critical processing boundary: sulfur-containing fumigants and halogenated vapours attack benzotriazole stabilizers and can produce embrittlement within 12–18 months, invalidating standard UV warranty conditions. After 3,000 h accelerated weathering per ISO 4892-3, the film should retain at least 75% of original elongation at break when tested per ISO 527-3. The stabilizer system of 7042 must be verified by lot because public technical bulletins do not disclose the exact antioxidant package used by the supplier.

Flexible packaging sealant webs: heat-seal onset, food-contact migration, and film-surface slip control

The sealant layer of BOPP/LLDPE laminates uses 7042 at 20–40 µm coating weight on extrusion lamination lines equipped with a 90 mm screw, L/D 30:1, melt temperature of 280–300 °C, and an air gap of 150–200 mm to obtain adhesion to primed BOPP or oriented PET. The low heat-seal initiation temperature, commonly 100–115 °C as measured by hot-tack testing per ASTM F1921, permits sealing through product contamination at packaging speeds above 60 cycles/min on horizontal form-fill-seal equipment. Seal strength is evaluated per ASTM F88 at 15–25 N/25 mm for 25 µm sealant film sealed at 135 °C jaw temperature and 0.35 MPa jaw pressure. Food-contact compliance for the final laminate is assessed under FDA 21 CFR 177.1520 and EU 10/2011/EC, with overall migration per EN 1186 below 10 mg/dm² and specific migration limits for erucamide and synthetic silica additives per EU 10/2011 Annex II. For the Chinese domestic market, GB 4806.7-2016 applies, with a total migration limit of 10 mg/dm² under prescribed simulant conditions. Slip performance is controlled by adding 2–4 wt% erucamide masterbatch at 5% active content and 1–2 wt% synthetic silica antiblock masterbatch at 10% active content, resulting in a kinetic coefficient of friction below 0.25 per ASTM D1894 after 24 h aging. Amine-based process aids or slip concentrates should be avoided because they can react with erucamide and shift the slip bloom rate, producing inconsistent seal initiation. The maximum continuous sealing temperature should remain below 160 °C; above this threshold, seal strength declines as the oriented film substrate begins to shrink and disrupt the seal interface.

When 7042 Replaces Conventional Butene LLDPE in High-Strength Agricultural Mulch Film

Thin-gauge agricultural mulch film at 8–25 µm exposes the drawdown capacity of 7042 to the melt-fracture boundary of the extruder and die. On a 45 mm smooth-bore single-screw extruder with a 150 mm die, a die gap below 1.0 mm and a melt temperature below 185 °C tend to induce shark-skin on the bubble surface; the standard corrective action is to raise melt temperature to 195–210 °C and open the die gap to 1.2 mm. The critical shear-rate boundary for visible surface melt fracture is equipment-specific and must be determined by on-line bubble-surface inspection at each die because published data for this CHN Energy Ningxia Coal grade in sub-15 µm monolayer structures is limited. The film is formulated with 1.5–3.0 wt% carbon black masterbatch for weed exclusion and 0.1–0.3 wt% UV stabilizer masterbatch. Elmendorf tear resistance is measured per ASTM D1922; machine-direction tear strength is maintained above 400 g at 25 µm gauge by limiting high-pressure LDPE content to 10–20 wt%, because excess LDPE raises modulus and causes brittle splitting at planting slits. Dart drop impact per ASTM D1709 Method A for 25 µm mulch film is typically not less than 80 g, but the value depends heavily on carbon black dispersion quality. Extended ultraviolet exposure requires the film to retain at least 50% of original elongation after 1,200 h under ISO 4892-2 conditions when a full-service-life mulch formulation is specified. The processing window narrows when the ambient extrusion hall temperature falls below 15 °C; frost-line instability and edge weave increase unless the air-ring chilling air is preconditioned to 20–25 °C.

Thermally stressed at freezer temperatures from -40 °C to -18 °C, 7042-based blown film at 40–100 µm is used for frozen vegetable bags and ice packaging. The butene-comonomer structure preserves puncture resistance at -30 °C when measured per ASTM D5748, provided the film is manufactured with a blow-up ratio of 2.5:1–3.0:1 and a die gap of 1.5 mm to limit excessive orientation. Additive loading is restricted to 2–3 wt% silica antiblock masterbatch and 1–2 wt% slip masterbatch; direct food-contact compliance per FDA 21 CFR 177.1520 and EU 10/2011 is required. Seal initiation at 105–120 °C supports vertical form-fill-seal lines running at 80–120 bags/min. The lower room-temperature stiffness of 7042 relative to HDPE limits unsupported bag width to about 400 mm when filling heads apply side loads; wider bags require gusseted construction or a HDPE-rich blend to prevent creasing and seal misalignment.

Surface-protection adhesive film substrates and corona treatment limits

For self-adhesive surface protection film, 7042 is coextruded as the backing layer at 30–60 µm; inline corona treatment to 38–42 mN/m is applied before the adhesive coating station, with wetting tension readout per DIN 53364 or ASTM D2578. The stabilizer package of 7042 must be verified to avoid migration into pressure-sensitive adhesives; published data for this specific CHN Energy Ningxia Coal grade in high-corona thin films is limited, so a 72 h adhesion retention test per ASTM D3330 is mandatory for each incoming lot. Corona levels above 42 mN/m promote oxidative species that can increase unwind force and adhesive transfer after accelerated aging at 40 °C and 90% relative humidity.